Dakota Ultrasonics MMX-6 User Manual

Page 36

Dakota Ultrasonics

An additional important consideration when measuring laminates, is that

any included air gaps or pockets will cause an early reflection of the

ultrasound beam. This effect will be noticed as a sudden decrease in

thickness in an otherwise regular surface. While this may impede accurate

measurement of total material thickness, it does provide the user with

positive indication of air gaps in the laminate.

•

Measuring Through Paint & Coatings

Measuring through paints and coatings are also unique, in that the

velocity of the paint / coating will be significantly different from the actual

material being measured. A perfect example of this would be a mild

steel pipe with approximately .025” of coating on the surface. Where the

velocity of the pipe is .2330 in/

sec, and the velocity of the paint is .0900

in/

sec. If the user is calibrated for mild steel pipe and measures

through both materials, the actual coating thickness will appear to be 2.5

times thicker than it actually is, as a result of the differences in velocity.

This error can be eliminated by using a special echo-echo mode to

perform measurements for applications such as these. In echo-echo

mode, the paint / coating thickness will be eliminated entirely and the

steel will be the only material measured.